Polyaxial bone anchoring device and system of an instrument and a polyaxial bone anchoring device

ABSTRACT

A bone anchoring device includes a receiving part having a first end with an end surface, a second end, a recess at the first end for receiving a rod, and a flexible head receiving portion at the second end for pivotably holding a head of a bone anchoring element, and a clamping ring positionable around the head receiving portion and movable from a first position where the head is pivotable relative to the receiving part, to a second position where the clamping ring exerts a radial force onto the head receiving portion to lock the head. The receiving part further includes a first engagement structure at or adjacent the end surface extending radially outwardly from an outer surface of the receiving part, such that a width of the receiving part including the first engagement structure is at least as wide as a maximum width of the clamping ring.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application claims the benefit of U.S. Provisional PatentApplication Ser. No. 62/379,115, filed Aug. 24, 2016, and claimspriority from European Patent Application EP 16 185 554.9, filed Aug.24, 2016, the contents of which are hereby incorporated by reference intheir entirety.

BACKGROUND Field

The present invention relates to a polyaxial bone anchoring device andto a system of an instrument and a polyaxial bone anchoring device. Thepolyaxial bone anchoring device comprises a receiving part for couplinga rod to a bone anchoring element and a clamping ring. The receivingpart has a flexible head receiving portion and the clamping ring isconfigured to be arranged around the head receiving portion. When theclamping ring is around the head receiving portion, the clamping ringcan assume a locking position wherein the clamping ring exerts a forceonto the head receiving portion such that an inserted head is locked,and a non-locking position wherein an inserted head is pivotablerelative to the receiving part.

Description of Related Art

US 2013/0085536 A1 describes a polyaxial bone anchoring device includinga receiving part with a rod receiving portion and a head receivingportion for introducing and clamping of the head of a bone anchoringelement and a locking ring configured to be arranged around the headreceiving portion. The locking ring includes an engagement structure inthe form of circumferentially extending ribs for engagement with a toolto allow the locking ring to be moved out of the locking position, i.e.releasing the locking mechanism. This enables a surgeon or otherpractitioner to carry out revisions or further positioning orre-positioning of the angular position of a receiving part with respectto the bone anchoring element.

US 2011/0060374 A1 describes a percutaneous access device which includesan inner tube and an outer tube and also describes a bone anchor havinga distal bone engaging portion and a receiving member having a recessfor receiving a spinal fixation element. The proximal end of thereceiving member may have an arcuate groove formed on an exteriorsurface thereof to facilitate connection of an instrument to thereceiving member.

SUMMARY

Embodiments of the invention provide a polyaxial bone anchoring devicethat allows an improved handling during surgery, and provide a systemincluding an instrument adapted for use with such a polyaxial boneanchoring device.

According to embodiments of the invention, a receiving part of apolyaxial bone anchoring device comprises a first engagement structureconfigured to be engaged by a corresponding engagement portion of aninstrument, wherein the first engagement structure is positioned on anouter surface of the receiving part directly at or adjacent to an endsurface of a top end of the receiving part. The end surface may forexample be an annular end surface of a leg of the receiving part formedby a rod receiving channel. The positioning of the engagement structuredirectly at or adjacent the first end allows to easily find a receivingpart and an aligned attachment position for an instrument in an incisionor hole formed in a tissue of a human body.

Due to such an arrangement of the first engagement structure, thereceiving part may be engaged by an instrument at a position moredistant away from an implant site in the bone and closer to theoperator. Accordingly, a need for sufficient space for the receivingpart and instrument within an incision or hole formed in the tissue ofthe human body may be reduced. In other words, less body tissue may beaffected by removal when creating the incision and a visual control ofoperation steps during surgery may be improved. If the engagementstructure is formed as a rib circumferentially extending along the endface, the instrument having a corresponding circumferential notch may beapplied to the receiving part with an easy find and rotation process.

The polyaxial anchoring device may further comprise a clamping ring,which, when moved relative to the receiving part in an axial direction,locks or unlocks the head of an anchoring element received in thereceiving part. In such an embodiment, there may further be provided asecond engagement structure arranged at upwardly projecting armsprovided at the clamping ring. Due to such arms, even the secondengagement structures may be in a position close to the top end and thefirst engagement portion of the receiving part. An instrument configuredto cooperate with the receiving part to effect locking and unlocking ofan anchoring element received in the receiving part may be provided witha corresponding engagement portion.

In a further embodiment, a third engagement structure of the receivingpart cooperates with a further engagement portion of the instrument. Thefurther engagement portion includes an abutment mechanism (a stop) andoptionally a self-locking mechanism. The abutment mechanism is realizedby an abutment face which serves as an endpoint of an engaging movement,while the self-locking mechanism may be realized by an inclined sectionof a guiding wall portion of the further engagement portion of theinstrument which creates an increasing amount of friction duringengagement by the third engagement portion.

The abutment mechanism allows to establish a correct alignment betweenthe instrument and the polyaxial bone anchoring device while theself-locking mechanism advantageously allows to maintain and control thelocked engaged position and to avoid unintentional disengagement.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features and advantages of the invention will become apparentfrom the description of embodiments by means of the accompanyingdrawings. In the drawings:

FIG. 1 shows an exploded perspective view of an embodiment of apolyaxial bone anchoring device according to the invention;

FIG. 2 shows a perspective view of the polyaxial bone anchoring deviceof FIG. 1 in an assembled state;

FIG. 3a shows a perspective view from the top of a receiving part ofFIG. 1;

FIG. 3b shows a perspective view from the bottom of the receiving partof FIG. 1;

FIG. 4a shows a cross-sectional view of the receiving part of FIGS. 3aand 3b along a line A-A in FIG. 4 c;

FIG. 4b shows an enlarged view of the head receiving portion of thereceiving part of FIG. 4 a;

FIG. 4c shows a top view of the receiving part of FIG. 4 a;

FIG. 4d shows a cross section of an upper part of the receiving part ofFIG. 4a in an enlarged view;

FIGS. 5a to 5d show a cross section, a top perspective view, a top viewand a bottom perspective view of a clamping ring of FIG. 1;

FIG. 6 shows a perspective view of multiple instruments according to anembodiment of the invention each engaging a polyaxial bone anchoringdevice according to FIG. 1;

FIG. 7 shows a perspective view of the instrument according to theembodiment and the polyaxial bone anchoring device in an engaged state;

FIGS. 8a to 8b show perspective views from the top and the bottom of theinstrument of FIG. 7;

FIGS. 9a to 9b show cross sectional views of the instrument of FIG. 7 intwo different views perpendicular to each other.

FIG. 10 shows an enlarged perspective view of a front end portion of theinstrument of FIG. 7;

FIG. 11 shows a view onto the front end portion of FIG. 10 along acentral axis of the instrument of FIG. 7;

FIG. 12 shows a side view of the inner wall surface of one of the legsof the front end portion of the instrument;

FIGS. 13a to 13d show steps of engaging the polyaxial bone anchoringdevice using the instrument of FIG. 7;

FIGS. 14a to 14b show cross sectional views of the instrument andpolyaxial bone anchoring device in an engaged state;

FIG. 15 shows an enlarged view of engagement portions and structures ofthe instrument and the polyaxial bone anchoring device in an engagedstate, respectively;

FIG. 16a shows a side view of the instrument and the polyaxial boneanchoring device in an engaged state;

FIG. 16b shows a horizontal cross sectional view taken along line B-B inFIG. 16 a;

FIG. 16c shows a horizontal cross sectional view taken along line C-C inFIG. 16 a;

FIGS. 17a to 17c show alternative embodiments of engagement structuresat a receiving part.

DETAILED DESCRIPTION

As shown in FIGS. 1 and 2, a bone anchoring device according to anembodiment of the invention includes a bone anchoring element 1 in theform of, for example, a bone screw having a shank 2 with a threadedportion and a head 3 with a spherically-shaped outer surface portion.The head 3 may have a recess 4 for engagement with a driver or tool. Thebone anchoring device also includes a receiving part 5 for receiving arod 6 to be connected to the bone anchoring element 1. Further, apressure member 7 may be provided in the receiving part 5 for exertingpressure onto the head 3 of the bone anchoring element 1. In addition,the bone anchoring device includes a clamping ring 8 that is mountableto the receiving part 5 for compressing a portion of the receiving part5 to exert pressure onto the pressure member 7 and in turn onto the head3. Lastly, the bone anchoring element also includes a fixation element 9in the form of, for example, an inner screw or set screw for fixing therod 6 in the receiving part 5.

The receiving part 5 will be described in greater detail referringadditionally to FIGS. 3a to 4d . The receiving part 5 includes first end5 a and an opposite second end 5 b and a central axis C that passesthrough the first end 5 a and the second end 5 b. The first end 5 a mayserve as an abutment for a portion of the instrument as described ingreater detail below. A passage 51 extends through the receiving part 5from the first end 5 a to the second end 5 b. The passage 51 may beformed as a cylindrical coaxial bore 51 a in a region from the first end5 a to a distance from the first end 5 a and may in this embodimentnarrow into an accommodation space 51 b with an inner diameter thatdecreases towards the second end 5 b until a region with a minimumdiameter is reached. The accommodation space 51 b serves foraccommodating head 3 of the bone anchoring element 1 and at least aportion of the pressure member 7, as can be seen also in FIGS. 14a, 14b. Adjacent the second end 5 b, a tapered or more specifically conicallyshaped bottom opening portion 51 c extends from the region having theminimum diameter.

A substantially U-shaped recess 52 extends from the first end 5 a in adirection of the second end 9 b wherein a width of the recess 52 isslightly larger than a diameter of the rod 6, such that the rod 6 can beplaced in the recess 52 and can be guided therein. The recess 52 forms achannel for the rod 6. By means of the recess 52, two free legs 52 a, 52b are formed, on which an internal thread 53 may be provided. In thisembodiment, the internal thread 53 extends from an annular end surface10 defined by first end 5 a up to a distance from the first end 5 ainside the bore 51. The internal thread 53 can be, for example, a metricthread, a flat thread, a negative angle-thread, a saw-tooth thread orany other thread form. Meanwhile, the fixation element 9 in the form ofan inner screw has a thread corresponding to the internal thread 53provided on the legs 52 a, 52 b. Preferably, a thread form such as aflat thread or a negative angle thread is used to prevent or reduce thesplaying of the legs 52 a, 52 b when the fixation element 9 isscrewed-in. An undercut 59 is formed adjacent to internal thread 53 in adirection away from the first end 5 a, as can be seen in FIG. 4 a.

An upper part 50 of the receiving part 5 which is adjacent to the firstend 5 a has a substantially cylindrical outer surface except for exampletwo flat recessed portions 56 a, 56 b, etc., which will be explained inmore detail below. Also, at the outer surface of the upper part 50 ofthe receiving part 5, a first engagement structure for engagement withthe instrument is provided, wherein the first engagement structure maybe formed by two circumferential ribs 54 a, 54 b which are formed oneach leg 52 a, 52 b in the embodiment shown, respectively. The ribs 54a, 54 b are positioned between the top end 5 a and a lower end 50 a ofthe upper portion 50. Each of the ribs 54 a, 54 b extends over a segmentof the circumference of the upper portion 50, for example, forapproximately a quarter circle or less, for example by an angle of about60° (see FIG. 4c ) as in the embodiment shown. The arrangement is suchthat one end 540 a 1, 540 b 1 of each rib 54 a, 54 b is positioned atthe recess 52 and the other end 540 a 2, 540 b 2 of each rib extendsapproximately to the middle section of each leg 54 a, 54 b as seen in acircumferential direction. Hence, in a circumferential direction, thereis a rib-free surface portion 55 a, 55 b on the outer surface of eachleg 52 a, 52 b which extends in that direction between the respectiveother end 540 a 2, 540 b 2 of the rib 54 a, 54 b and a respective otheredge of U-shaped recess 52.

Furthermore, the ribs 54 a, 54 b are arranged in an asymmetric mannerwith respect to a plane extending through the central axis C of thecoaxial bore 51 and a longitudinal axis L of the recess 52. Morespecifically, the position of the ribs 54 a, 54 b is offset by 180°measured in relation to the central axis C and is rotated with respectto the central axis C such that the rib 54 a of the leg 52 a extends tothe rod receiving recess 52 at one side of the receiving part 5 and therib 54 b extends to the rod receiving recess 52 at the other side of thereceiving part 5. This permits the instrument to be placed first ontothe rib-free portions 55 a, 55 b and then to be rotated to engage theribs 54 a, 54 b as described in greater detail below.

The ribs 54 a, 54 b may have a substantially rectangular cross-sectionor any other shape, but as can be seen in FIGS. 4a and 4d , adovetail-shape which in this embodiment is single-sided is preferable.Namely, the ribs 54 a, 54 b include a horizontal upper surface 141 whichextends substantially perpendicular to the central axis C, while abottom surface 142 is inclined and extends radially downwards, i.e.,towards the distal direction. In other words, a width of the ribs 54 a,54 b increases in a direction radially outwards (as seen from thecentral axis C) allowing for a more stable and reliable connection withthe instrument when a corresponding complementary profile is alsoprovided therein. The horizontal upper surface 141 in this embodiment isflush with the annular end surface 10 of the legs 52 a, 52 b of thereceiving part 5 which is provided at the first end 5 a. Nevertheless,in an alternative embodiment illustrated in FIG. 17a , ribs 54′ ofmodified receiving part 5′ may also have a full two-sideddovetail-shape. The annular end surface 10 needs not to be planar. Itmay have an inclination directed inwards or outwards, or may be rounded.In preferred embodiments, the upper surface of the ribs 54 a, 54 b, 54′forming the first engagement structure is continuous with the annularend surface 10.

In any case, the ribs 54 a, 54 b and 54′ in these embodiments arearranged directly at the annular end surface 10 of the legs 52 a, 52 bdefined by the first end 5 a of the receiving part 5, 5′ or at leastadjacent to that annular end surface 10 at first end 5 a. Protrusions orrecesses formed in the annular end surface are not ruled out, as long asthe annular end surface 10 at first end 5 a may serve as an abutmentsurface for the instrument as described below. A distance of the uppersurface 141 of the ribs 54 a, 54 b from the annular end surface 10 ofless than a width of the ribs in a direction parallel to the centralaxis C may be acceptable and is covered by the term “adjacent”.

An advantage of the arrangement of ribs 54 a, 54 b at the top of thereceiving part 5 directly at or adjacent to an annular end surface 10 atthe first end 5 a arises from the fact that the engagement features ofthe bone anchoring device are positioned away from the bone surface whenthe anchoring element is implanted within the bone and the head of theanchoring element is received in the accommodation space of thereceiving part. This in turn allows that the instrument engages thedevice remote from the bone surface which avoids damages to the bodytissue and permits to create small incisions. Also, this structure ofthe receiving part allows the engaging instrument to be configured morestable and sustainable, which will become clear from explanations withregard to the instrument below.

It is noted that the ribs may also have a substantially rectangular,trapezoidal, rhomboid-shaped, tooth-shaped or rounded cross-section,etc., or with regard to further modified receiving parts 5″, 5′″, theribs 54″, 54′″ may even have complex shapes as illustrated in FIG. 17bor 17 c, respectively. The ribs 54 a, 54 b may have inclined or roundedend portions. It shall be understood that a number of ribs is notlimited to just one per leg 52 a, 52 b. More ribs may be implementedbelow the ribs 54 a, 54 b, such as stop ribs 54 a′, 54 b′ as examples ofthird engagement structures.

Stop ribs 54 a′, 54 b′ have a length less than that of the ribs 54 a, 54b as can be seen in FIGS. 3a, 3b . Nevertheless, similar to ribs 54 a,54 b, stop ribs 54 a′, 54 b′ extend from the rod receiving recess 52 atrespective sides of the receiving part 5, and also extend in a distanceand parallel to ribs 54 a, 54 b in a circumferential direction on thecylindrical outer surface of upper part 5. The cross section of stopribs 54 a′, 54 b′ is in this embodiment rectangular as can be seen inFIG. 4a , but the same shapes as detailed with regard to ribs 54 a, 54 bare possible as well. Stop ribs 54 a′, 54 b′ may also include roundedand/or inclined end portions. The width may be equal to or less thanthat of ribs 54 a, 54 b, or may even be larger. In this embodiment, thewidth of stop ribs 54 a′, 54 b′ is smaller than that of ribs 54 a, 54 b.The stop ribs 54 a′, 54 b′ are arranged directly at or adjacent to anupper end wall 561 of recessed surface portions 56 a, 56 b.

As noted, the outer surface of the receiving part 5 also includes thesubstantially flat or planar recessed portions 56 a, 56 b. Recessedportions 56 a, 56 b are positioned at the upper part 50 in acircumferential direction in correspondence with the circumferentiallyextending ribs 54 a, 54 b and extend from an edge 50 a at a bottom endof upper part 50 in a proximal direction parallel to the central axis Cup to a predetermined distance from the ribs 54 a, 54 b. The recessedportions 56 a, 56 b need not have a planar flat surface recessed from acylindrical outer contour of the receiving part 5 as in the embodimentbut may also be rounded and/or provided with side walls. The recessedportions 56 a, 56 b serve as a guiding surface for upwardly projectingarms 83 a, 83 b of clamping ring 8 as will be detailed below.

Between the upper part 50 and the second end 5 b of the receiving part 5a head receiving portion 57 of the receiving part 5 is provided thatincludes the accommodation space 51 b. The head receiving portion 57also has a substantially cylindrical outer surface that has a smallerdiameter than the diameter of the upper part 50 of the receiving part 5.Adjacent the second end 5 b, there is a portion 57 a of the outersurface that slightly tapers outwards. To allow insertion of the head 3,the head receiving portion 57 is flexible. In the embodiment shown, thehead receiving portion 57 includes a plurality of flexible wall sections57 b that are separated by slits 58 extending in a longitudinaldirection and being open towards the second end 5 b. According toembodiments, the slits 58 may or may not extend even up into the upperpart 50 of receiving part 5, as can be seen in FIGS. 3a and 3b . Thenumber and size of the slits 58 is provided depending on the desiredflexibility of the head receiving portion 57.

An inner diameter of the passage 51 at the second end 5 b is smallerthan a diameter of the head 3 of anchoring element 1. Due to theflexibility of the head receiving portion 57 the head 3 could beinserted from the second end 5 b, but with the clamping ring 8 arrangedin place embracing the head receiving portion 57, there is notsufficient expansion of the flexible wall sections 57 b to allowinsertion from the bottom end. In use, the anchoring element 1 in thisembodiment will rather be inserted into the receiving part 5 via firstend 5 a (i.e., top loading).

The clamping ring 8 will be described in greater detail referringadditionally to FIGS. 5a to 5 d.

The clamping ring 8 comprises an upper end or first end 8 a and anopposite lower end or second end 8 b and may have a substantiallyspherical outer surface 81 which narrows towards the second end 8 b. Theouter diameter of the spherical surface 81 at or adjacent the first end8 a may be such that when the clamping ring 8 is mounted around the headreceiving portion 57 of the receiving part 5, the outer sphericalsurface 81 of the clamping ring and the outer cylindrical surface of theupper part 50 of the receiving part 5 are flush with each other asdepicted, for example, in FIG. 2. An inner diameter of the clamping ring8 is such that the clamping ring 8 can be mounted around the headreceiving portion 57 wherein the upper end 8 a faces towards the bottomend or edge 50 a of the upper part 50 of the receiving part 5. Alignmentfeatures in the form of flat portions 82 are provided at the outersurface 81 of the clamping ring 8. The flat portions 82 are offset by180°. The alignment features may assist in aligning the clamping ring 8correctly with respect to the receiving part 5, in particular withrespect to further flat surfaces 50 b recessed from the cylindricalouter surface of upper part 50 directly below the U-shaped recess 52,see FIG. 3a . It shall be noted, however, that the shape of the outersurface of clamping ring 8 may be different in other embodiments. Forexample, the outer surface 81 may have a cylindrical shape etc.

As can be seen in particular in FIG. 5a , clamping ring 8 further has afirst inner cylindrical surface portion 86 that is adjacent orsubstantially adjacent to the upper end 8 a. There may be a smallinclined surface or beveled surface (not shown) provided adjacent to theupper end 8 a to facilitate mounting. Adjacent or substantially adjacentto the lower end 8 b, a second inner surface portion 87 of the clampingring 8 may be tapered in such a manner that the inner diameter conicallywidens towards the lower end 8 b. The second inner surface portion 87 isconfigured to cooperate with the outer surface portion 57 a of the headreceiving portion in such a manner that when the clamping ring 8 ismoved towards a lowermost position on the head receiving portion 57, thecooperating surfaces 57 a of the head receiving portion 57 and 87 of theclamping ring 8 exert an increasing inwardly directed radial forcetowards the head 3. Moreover, a height of the ring-shaped base portion(between ends 8 a, 8 b, i.e., without arms 83 a, 83 b) of clamping ring8 in an axial direction, as can be seen in FIGS. 14a and 14b ,corresponds substantially to a height of the head receiving portion 57of the receiving part 5.

The clamping ring 8 includes two upwardly projecting arms 83 a, 83 bextending from a shoulder 85 formed at first end 8 a. As can be seenparticularly in FIGS. 2, 14 a and 14 b, the length of arms 83 a, 83 bsubstantially corresponds to a length of recessed portions 56 a, 56 b(as measured from the edge 50 a at the bottom end of upper part 50) in adirection parallel to the central axis C, which are arranged toslideably receive arms 83 a, 83 b, when the clamping ring 8 is attachedto the receiving part. Each of arms 83 a, 83 b has end faces 89 whichmay abut on—or at least may approach close to—upper end wall 561 of therecessed portions 56 a, 56 b. Similarly, the width of arms 83 a, 83 bsubstantially corresponds to that of recessed portions 56 a, 56 b. Thetwo arms 83 a, 83 b are located diametrically opposite to each other andare positioned asymmetrically with respect to the flat portions 82. Morespecifically, the position of both arms 83 a, 83 b is rotated in thesame direction by for example about 60° in this non-limiting embodimentwith respect to flat portions 82 in the circumferential direction, whichis indicated in FIG. 5c by the dash-dotted axis R that will be alignedwith longitudinal axis L of the U-shaped recess 52 in an assembledstate.

Each of the two upwardly projecting arms 83 a, 83 b includes anengagement structure for engagement with an instrument on its outersurface within or adjacent a tip portion of the respective arm which inthis embodiment is provided as a dovetail-shaped circumferentiallyextending engagement structure formed as a notch 88 a, 88 b. As alreadynoted above a consequence of such positioning at a tip portion of thearms 83 a, 83 b, the engagement structure of the clamping ring 8 as wellas the engagement structure of the receiving part are located (i) closeto each other and (ii) at a portion of a respective piece most proximateto the first end 5 a of the receiving part 5 and away from the headreceiving portion 57, i.e., away from the bone surface when thepolyaxial bone anchoring device is in an assembled state in-situ. Thisallows to require less space within the body tissue by an instrument forperforming steps of intermittent locking/unlocking during, e.g.,repositioning of single vertebra or readjusting of a receiving part withan unlocked rod, wherein the clamping ring 8 is engaged and axiallydisplaced by for example an outer tube of a locking/unlocking instrumentwith respect to an inner tube of the locking/unlocking instrument, whichengages the receiving part 5. Examples of a similar instrument that canbe used for locking and releasing a lock on a bone anchoring device, andsimilar interactions of such an instrument with other bone anchoringdevices, are disclosed in U.S. Provisional Patent Application Ser. No.62/371,029 and European Patent Application EP 16 182 818.1, the contentsof which are hereby incorporated by reference in their entirety.

According to embodiments of the invention, the arms 83 a, 83 b have asufficient length that the engagement structures provided on the arms,such as notches 88 a, 88 b, are arranged at an axial position in thedirection of the central axis C corresponding to that of the rod 6 whenthe rod is received in the U-shaped recess 52 and pressed against thepressure member 7 (i.e., in a locked state of the bone anchoringdevice), preferably even at or above an axial position of a largestdiameter of the rod 6 like in the embodiment illustrated herein, seeFIGS. 14a , 14 b.

In compliance with the dovetail-shaped cross sectional profile, a widthof notches 88 a, 88 b decreases in a direction radially outwards towardsthe outer surface of arms 83 b. The notches 88 a, 88 b include acylindrical base surface 880 coaxial with the central axis C andcorrespondingly inclined bottom surfaces 881 and upper surfaces 882 ascan be seen in more detail in FIG. 5a . It is noted that the engagementstructure provided at the arms 83 a, 83 b need not be a notch 88 a, 88 bbut may also be provided as a protruding rib as in the case of ribs 54a, 54 b. Also, the cross sectional profile of the engagement structureformed as notches 88 a, 88 b or ribs may be substantially rectangular,trapezoidal, rhomboid-shaped, tooth-shaped or rounded, etc. instead ofbeing dovetail-shaped.

A length of the engagement structures, e.g., notches 88 a, 88 b, islimited to the width of the arms 83 a, 83 b and substantiallycorresponds to that of the engagement structures of the receiving part,i.e., the circumferential ribs 54 a, 54 b. A depth of the recessedportions 56 a, 56 b and a thickness of the arms measured in radialdirection is defined such that the cylindrical base surface 880 ofnotches 88 a, 88 b is substantially flush with the cylindrical outersurface of the receiving part 5, when the clamping ring is assembledwith the receiving part. As a consequence, a dovetail-shapedcircumferentially extending rib as an example of an engagement portionin an outer tube of the locking/unlocking instrument may be smoothlyslid into a corresponding notch 88 a, 88 b of the clamping ring 8.However, a small step between the cylindrical outer surface of thereceiving part 5 and base surface 880 of the notches 88 a, 88 b is notruled out. Furthermore, it is not ruled out that further notches or ribsare provided at arms 83 a, 83 b.

The pressure member 7 as shown in FIGS. 1 and 14 a, 14 b comprises asubstantially cylindrical outer surface 71 which has a diameter that isequal to or slightly smaller than an inner diameter of the cylindricalcoaxial bore 51 a to facilitate sliding and accommodation therein.Pressure member 7 also has a rod receiving portion 72 which iscylinder-segment shaped for receiving a rod 6 therein and which formstwo legs opposite each other, which face the first end of the receivingpart when the pressure member 7 is inserted in the coaxial bore 51 a.Moreover, a spherical hollow section 73 is formed at a lower end ofpressure member 7 which contacts the head 3 of anchoring element 1 andmay exert pressure transferred from an inserted rod 6 onto the head 3 tolock the same when for example fixation element 9 is tightened. Thepressure member may further comprise a coaxial hole allowing access torecess 4 which is provided in the head 3 of anchoring element 1.

The receiving part 5, the clamping ring 8, the pressure member 7, thefixation element 9 and the bone anchoring element 1 may be made ofbio-compatible materials, for example of titanium or stainless steel, ofa bio-compatible alloy, such as a NiTi-alloys, for example Nitinol,magnesium or magnesium alloys or from a bio-compatible plastic material,such as, for example, polyether ether ketone (PEEK) or poly-1-lactideacid (PLLA). The parts can be made of the same or of differentmaterials.

In operation, the polyaxial bone anchoring device 100 is first assembledby attaching the clamping ring 8 to the flexible head receiving portion57 via the second end 5 b, wherein the flexible wall sections 57 b areslightly compressed by the first and second inner surface portions 86,87 of the clamping ring 8. Also, the bone anchoring element 1 isinserted into the receiving part 5 via the first end 5 a. The pressuremember 7 may then also be slid into the coaxial bore 51 a of receivingpart 5, and the anchoring element 1 is applied to a bone using, e.g., adriver or tool. A rod 6 may then be guided into the U-shaped recess 52of receiving part 5 and using a locking/unlocking instrument theclamping ring is axially moved in the distal direction away from thefirst end 5 a towards a lowermost position on the head receiving portion57 to clamp the head 3, wherein the conical second inner surface portion87 of clamping ring 8 cooperates with the outer surface portion 57 a ofthe head receiving portion in such a manner that an increasing inwardlydirected radial force is exerted towards and onto the head 3.

Thereby, the fixation element 9 needs not to be tightened yet. Rather, alocking/unlocking instrument allows a temporary clamping and/orunclamping via the actuating, i.e., moving clamping ring between aclamping position and a pre-locking position. This function permits theoperator to readjust and fix an angular position of the receiving partwith respect to the anchoring element even without an inserted rod, orto reposition individual vertebrae via the attached instrument.Nevertheless, final fixation will be effected by tightening the fixationelement 9 and thus pressing the pressure member 7 against the head 3 tolock the same.

Next, an instrument 200 for use with the polyaxial bone anchoring device100 will be explained with reference to FIGS. 6-12. The instrument 200functions as a head extension device which is configured to be attachedto the receiving part 5 in-situ and thereby allows manipulating thereceiving part 5 or supplying further instruments and/or parts to thereceiving part 5. Multiple such instruments 200 may be attached torespective polyaxial bone anchoring devices 100 in-situ as illustratedin FIG. 6, the polyaxial bone anchoring devices 100 being positionedwithin vertebrae, respectively. Unlike the above explained instrumentfor locking/unlocking the clamping ring 8, which also engages theclamping ring 8 in addition to the receiving part 5, the instrument 200is arranged to only engage the ribs 54 a, 54 b at the receiving part.Nevertheless, embodiments of any instruments such as the above describedlocking/unlocking instrument that are also configured to engagereceiving part 5 of polyaxial bone anchoring device 100 disclosed hereinare encompassed by the appended claims.

The instrument 200 includes a tubular member 202 having a front endportion 204, which comprises engagement portions for engagement with theengagement structures of the receiving part, and a rear end portion 206as can be seen in FIG. 7.

As shown in FIGS. 8a-9b , the tubular member 202 includes an inner bore212 extending from the rear end portion 206 to the front end portion204, and the front end portion 204 is provided with a substantiallyrectangular-shaped recess 214 into which the bore 212 opens, and whichforms two free legs 214 a, 214 b. The inner bore 212 has a diametersmaller than that of the receiving part 5. Inner bore 212 ends at anannular abutment surface 217, which serves to abut on annular endsurface 10 of receiving part 5 during engagement. The tubular member 202further has recessed portions 210 at opposite sides thereof in a regionof the rear end portion 206, which may serve for attaching furtherinstruments or for gripping the instrument.

As can be seen in FIG. 10, the legs 214 a, 214 b each includes a roundedtip portion 215 a, 215 b, respectively, which facilitates insertion ofthe instrument into the incision or hole in the tissue and guiding tothe in-situ position of the receiving part 5. A length of the roundedtip portion 215 a, 215 b in a direction of a central axis T of theinstrument is small compared to the portion of the free legs which has asubstantially cylindrical contour and constant width measured in aradial direction from the central bore 212.

At an inner surface of the instrument in a region of the tip portion 215a, 215 b of the free legs of the frond end portion 214 there areprovided two engagement portions in the form of notches 216 a, 216 b.These notches 216 a, 216 b have a single-sided dove-tail-shaped crosssection, which is complementary to that of the ribs 54 a, 54 b providedat the receiving part 5. Notches 216 a, 216 b are configured toslideably receive the ribs 54 a, 54 b during engagement by rotation in acircumferential direction as will be detailed below. Notches 216 a, 216b extend between the recess walls and open into the recess 214 on bothsides thereof in the circumferential direction around central axis T andhave a length which corresponds to that of ribs 54 a, 54 b, covering forexample an angle of 45°. As with regard to ribs 54 a, 54 b, the crosssection may be different from a (single sided) dovetail-shape. Also thelength may vary and depends on the width of the legs 214 a, 214 b.

Moreover, second engagement portions in the form of stop notches 218 a,218 b are provided directly at the edge of the tip portions 215 a, 215 bextending from the recess at one open end 220 a thereof in acircumferential direction around central axis T. More specifically, thenotches 218 a, 218 b have a length shorter than that of notches 216 a,216 b. As a consequence, stop notches 218 a, 218 b include an end orabutment face 220 b facing in a circumferential direction, in thisembodiment facing in the counter-clockwise direction in both cases.

Stop notches 218 a, 218 b are configured to slideably receive stop ribs54 a′, 54 b′ therein during engagement by rotation in a circumferentialdirection as will be detailed below. However, as a consequence of theabutment faces 220 b, rotational movement of the instrument 200 withrespect to the receiving part 5 is limited by these abutment faces 220 bfunctioning as a stop. Advantageously, such stop guarantees that theinstrument 200 attains a correctly aligned engagement position withrespect to the receiving part 5 and does not unintentionally losecontact with the receiving part during use, which otherwise might beharmful for the patient and also might damage the engagement features.

Still further, as can be seen in FIG. 10, the stop notches 218 a, 218 bdo no need to have a lower wall. Rather, the notches 218 a, 218 b arealso open towards the distal direction, i.e., towards second end 5 b ofreceiving part 5. Since an axial position of the instrument 200 withrespect to the receiving part 5 is already defined by ribs 54 a, 54 breceived in notches 216 a, 216 b, the lower walls can be omitted and thestop notches 218 a, 218 b herein merely provide for the stop function.Due to the omission of the lower walls, the tip edge of instrument 200is further closer to the ribs 54 a, 54 b seen in the axial direction,which further reduces the depth with which the instrument has to enterthe incision in order to engage the receiving part. This feature furtheravoids delicate parts arranged near the tip and the engagement portionswhich inevitably undergo large lever actions during use.

As can be seen in FIG. 12, the stop notches nevertheless have an upperguiding wall, which, however, has two sections, namely an annularhorizontal section 221 which extends in a plane perpendicular to thecentral axis T, and an inclined section 222. The horizontal section 221is located extending from the open end 220 a of notches 218 a, 218 b,while the inclined section 222 extends adjacent to horizontal section221 up to the abutment face 220 b at the other end of notches 218 a, 218b. The inclination is such that the width of notches 218 a, 218 bnarrows towards the abutment end 220 b. As a consequence, duringsliding-in of a rib 54 a′, 54 b′ received in one of the notches 218 a,218 b from the open end 220 a in a rotational movement towards theabutment face 220 b, such rib 54 a′, 54 b′ eventually contacts theinclined surface which in turn creates a frictional force between therib 54 a′, 54 b′ and the inclined surface 222.

Advantageously, this function on the one hand assists in maintaining anengaged state of the instrument 200 with the receiving part 5 andprevents unintentional loosening. On the other end, the operator obtainsa tactile response during the rotational movement of the instrument thathe is approaching the stop.

It is noted that between the notches 54 a and 54 a′ as well as betweennotches 54 b and 54 b′ there extends a cylindrical inner surface 219,which as compared with the inner surface of inner bore 212 has anenlarged diameter, which corresponds to the diameter of the outercylindrical surface of the upper part 50 of the receiving part 5. Thiscylindrical inner surface 219 serves for guiding the instrument whileplacing the instrument on the receiving part 5 as will be explained inthe following.

A use of the instrument 200 and the polyaxial bone anchoring device 100is shown in FIGS. 13a-d . As shown in FIG. 13a the instrument 200 ismoved to the receiving part 5 in a direction of the central axes C, Tbeing aligned with each other. Thereby, the free legs 214 a, 214 b arealigned with the rib-free portions 55 a, 55 b of the receiving part 5,respectively, in a circumferential direction.

In FIG. 13b , the instrument 200 is guided over the receiving part 5.The cylindrical inner surface 219 of the instrument 200 slideablycontacts the outer cylindrical surface of the upper part of thereceiving part 5 and crosses the rib-free portions 55 a, 55 b.

In FIG. 13c , the downward movement of the instrument 200 stops whereinthe annular abutment surface 217 at the end of bore 212 abuts on theannular end surface 10 of the receiving part. The rounded tip portion215 a, 215 b having the engagement portions arranged at its inner wallis in this situation located at an axial position of the engagementstructures 54 a, 54 b, 54 a′, 54 b′.

In FIG. 13d , the instrument 200 is rotated in the circumferentialdirection as indicated by the arrow. Thereby, the ribs 54 a, 54 b of thereceiving part 5 slide with leading end portions 540 a 2, 540 b 2 intothe respective notches 216 a, 216 b of the instrument 200, and the ribs54 a′, 54 b′ slide with leading end portions 540 a 2′, 540 b 2′ into therespective notches 218 a, 218 b of the instrument 200. Initially, theinclined surface 222 has contacted an upper surface of ribs 54 a′, 54 b′creating an increasing friction and slight tension between the ribs 54 aand 54 a′ as well as 54 b and 54 b′. Finally, leading end portions 540 a2′, 540 b 2′ of each of ribs 54 a′, 54 b′ abuts on respective abutmentfaces 220 b. The increasing friction thereby leads to self-locking ofthe engagement between the receiving part 5 and the instrument, wherebythe abutment serves to define an aligned endpoint of the rotationalmovement.

In this final engagement position, which is also shown in FIGS. 14a and14b , the operator may perform desired steps of assembling and orientingthe polyaxial bone anchoring device. FIG. 15 shows an enlarged detail ofthe engagement structures and portions. FIGS. 16b and 16c revealhorizontal cross sections in the engaged position.

Various modifications may be made without departing from the scopedefined by the appended claims. For example, as noted above, theinstrument may be different from the head extension instrument and mayfor example be a locking/unlocking instrument.

Moreover, the polyaxial bone anchoring device may include a pressuremember formed as an inner cap itself having a flexible head receivingportion as described for example in European Patent Application EP 16182 818.1, wherein a head of an anchoring element may be loaded to ahead receiving portion of a receiving part from the bottom. In thatcase, the ribs disclosed therein for example in FIG. 3 are replaced withan arrangement of ribs as explained above while all other features aremaintained.

However, it may also be conceived to add arms 83 a, 83 b as describedabove to the clamping ring disclosed in European Patent Application EP16 182 818.1 to bring the ribs of the clamping ring and the receivingpart into closer proximity like in the embodiment presented above.

While the present invention has been described in connection withcertain exemplary embodiments, it is to be understood that the inventionis not limited to the disclosed embodiments, but is instead intended tocover various modifications and equivalent arrangements included withinthe spirit and scope of the appended claims, and equivalents thereof.

What is claimed is:
 1. A bone anchoring device comprising: a receivingpart for coupling a rod to a bone anchoring element, the receiving partcomprising a first end, a second end, a central axis extending betweenthe first end and the second end, an end surface at the first end thatfaces away from the second end, a recess at the first end for receivingthe rod, and a head receiving portion at the second end for pivotablyholding a head of the bone anchoring element, the head receiving portionbeing at least partially flexible; and a clamping ring positionablearound the head receiving portion, wherein when the clamping ring isaround the head receiving portion, a maximum width of the clamping ringmeasured perpendicular to the central axis is at least as wide as everyother width of the clamping ring measured perpendicular to the centralaxis, and the clamping ring is movable from a first position wherein aninserted head is pivotable relative to the receiving part, to a secondposition wherein the clamping ring exerts a radial force onto the headreceiving portion to lock the inserted head relative to the receivingpart while the recess for the rod remains vacant or unobstructed;wherein the receiving part further comprises a first engagementstructure configured to be engaged by an instrument, wherein the firstengagement structure is positioned at or adjacent to the end surface atthe first end and extends radially outwardly from an outer surface ofthe receiving part, such that a width of the receiving part measuredperpendicular to the central axis and including the first engagementstructure is at least as wide as the maximum width of the clamping ring.2. The bone anchoring device of claim 1, wherein the clamping ringcomprises a second engagement structure configured to be engaged by theinstrument to facilitate axial displacement of the clamping ringrelative to the receiving part.
 3. The bone anchoring device of claim 2,wherein the clamping ring comprises an upwardly projecting arm, andwherein the second engagement structure is at the upwardly projectingarm.
 4. The bone anchoring device of claim 3, wherein the secondengagement structure is at a region of a free end of the upwardlyprojecting arm, and wherein the upwardly projecting arm has a lengthsuch that the second engagement structure is positioned in a directionalong the central axis that is at or above a position of the rod whenthe rod is held in the recess of the receiving part.
 5. The boneanchoring device of claim 4, wherein the receiving part furthercomprises a recessed portion extending axially up to a distance from thefirst end of the receiving part for accommodating the upwardlyprojecting arm of the clamping ring.
 6. The bone anchoring device ofclaim 1, wherein the clamping ring comprises an upwardly projecting arm.7. The bone anchoring device of claim 1, wherein at least one surface ofthe first engagement structure has a dovetail-shaped cross-section. 8.The bone anchoring device of claim 1, wherein the first engagementstructure extends farther radially outwardly than all other portions ofthe receiving part.
 9. The bone anchoring device of claim 1, wherein asurface of the first engagement structure that faces away from thesecond end of the receiving part is flush with the end surface at thefirst end of the receiving part.
 10. The bone anchoring device of claim1, wherein the end surface at the first end of the receiving part formsan annular-segment shaped end surface of legs formed by the recess. 11.The bone anchoring device of claim 1, further comprising a pressuremember positionable in the receiving part and configured to exertpressure on the head when the head is held in the head receiving portionof the receiving part.
 12. The bone anchoring device of claim 1, whereinthe first engagement structure is arranged asymmetric with respect to aplane extending through the central axis of the receiving part andthrough a longitudinal axis of the recess.
 13. The bone anchoring deviceof claim 1, wherein the receiving part further comprises a thirdengagement structure which is aligned with the first engagementstructure in the circumferential direction and is spaced apart axiallyfrom the first engagement structure, and wherein the third engagementstructure comprises a circumferentially facing abutment end.
 14. Asystem comprising the bone anchoring device of claim 13 and aninstrument comprising at least one tubular member comprising: a firstengagement portion formed as a notch for engaging the first engagementstructure at the receiving part; and a second engagement portion forengaging the third engagement structure at the receiving part, whereinthe second engagement portion comprises an abutment face for facing andabutting against the abutment end of the third engagement structure whenthe first engagement structure and the first engagement portion areengaged.
 15. The system of claim 14, wherein the second engagementportion of the instrument further comprises a guiding wall with aninclined section with respect to the circumferential direction toprovide a self-locking mechanism.
 16. A system comprising the boneanchoring device of claim 1 and an instrument comprising at least onetubular member comprising a first engagement portion formed as a notchfor engaging the first engagement structure at the receiving part. 17.The system of claim 16, wherein the first engagement structure isconfigured to be engaged by the instrument via a rotational movement ofat least part of the instrument in a circumferential direction aroundthe central axis.
 18. A method for coupling a rod to a bone via a boneanchoring device comprising a bone anchoring element comprising a shankfor anchoring to bone and a head, a receiving part comprising a firstend, a second end, a central axis extending between the first end andthe second end, an end surface at the first end that faces away from thesecond end, a recess at the first end for receiving the rod, and a headreceiving portion at the second end for pivotably holding the head ofthe bone anchoring element, the head receiving portion being at leastpartially flexible, a clamping ring positionable around the headreceiving portion, wherein when the clamping ring is around the headreceiving portion, a maximum width of the clamping ring measuredperpendicular to the central axis is at least as wide as every otherwidth of the clamping ring measured perpendicular to the central axis,and the clamping ring is movable from a first position wherein aninserted head is pivotable relative to the receiving part, to a secondposition wherein the clamping ring exerts a radial force onto the headreceiving portion to lock the inserted head relative to the receivingpart, and a fixation element, wherein the receiving part furthercomprises a first engagement structure configured to be engaged by aninstrument, wherein the first engagement structure is positioned at oradjacent to the end surface at the first end and extends radiallyoutwardly from an outer surface of the receiving part, such that a widthof the receiving part measured perpendicular to the central axis andincluding the first engagement structure is at least as wide as themaximum width of the clamping ring, the method comprising: inserting theshank of the bone anchoring element into bone; pivoting the receivingpart relative to the bone anchoring element when the head is in the headreceiving portion and the clamping ring is around the head receivingportion at the first position; locking the head relative to thereceiving part while the recess for the rod remains vacant orunobstructed or while the rod is in and remains movable in the recess;and urging the rod axially in the recess towards the head with thefixation element to lock the rod relative to the receiving part.
 19. Themethod of claim 18, further comprising attaching an instrument to thereceiving part by advancing the instrument over the receiving part androtating the instrument relative to the receiving part to engage theinstrument with the first engagement structure.
 20. A bone anchoringdevice comprising: a receiving part for coupling a rod to a boneanchoring element, the receiving part comprising a first end, a secondend below the first end, a central axis extending between the first endand the second end, an end surface at the first end that faces away fromthe second end, a recess extending from the first end to a bottom forreceiving the rod, and a head receiving portion at the second end forpivotably holding a head of the bone anchoring element, the headreceiving portion being at least partially flexible; a pressure memberpositionable in the receiving part to a same axial height as the bottomof the recess and configured to exert pressure on the head when the headis held in the head receiving portion of the receiving part; and aclamping ring positionable around the head receiving portion, whereinwhen the clamping ring is around the head receiving portion, theclamping ring is movable from a first position wherein an inserted headis pivotable relative to the receiving part while the entire clampingring remains below the first end of the receiving part, to a secondposition wherein the clamping ring exerts a radial force onto the headreceiving portion to lock the inserted head relative to the receivingpart; wherein the receiving part further comprises a first engagementstructure configured to be engaged by an instrument, wherein the firstengagement structure is positioned at or adjacent to the end surface atthe first end and extends radially outwardly from an outer surface ofthe receiving part.
 21. A bone anchoring device comprising: a receivingpart for coupling a rod to a bone anchoring element, the receiving partcomprising a first end, a second end, a central axis extending betweenthe first end and the second end, an end surface at the first end thatfaces away from the second end, a recess extending from the first end toa bottom for receiving the rod, and a head receiving portion at thesecond end for pivotably holding a head of the bone anchoring element,the head receiving portion being at least partially flexible; and aclamping ring positionable around the head receiving portion, whereinwhen the clamping ring is around the head receiving portion, theclamping ring is movable from a first position wherein an inserted headis pivotable relative to the receiving part, to a second positionwherein the clamping ring exerts a radial force onto the head receivingportion to lock the inserted head relative to the receiving part;wherein the receiving part further comprises an outer surface at thefirst end, at least part of the outer surface extendingcircumferentially around the central axis at a first radial distancefrom the central axis and at least part of the outer surface extendingfrom the first end to a position closer axially to the bottom of therecess than to the first end at the first radial distance, and a firstengagement structure that extends radially outwardly from the outersurface for engagement with an instrument; wherein the first engagementstructure is at or adjacent to the end surface at the first end, ispositioned axially between a first exposed part of the outer surface andthe end surface at the first end, and is at a same axial height as asecond exposed part of the outer surface, and wherein the second exposedpart of the outer surface remains spaced apart from the clamping ringwhen the clamping ring is around the head receiving portion.
 22. Thebone anchoring device of claim 21, wherein the first engagementstructure and the first exposed part of the outer surface are atdifferent circumferential positions relative to the central axis.